How to point already declared javascript function to a variable

Question

If I wanted to first declare a function, and then at some point I want to reference the function and not its return value to a variable, how would I do that?

var best = bestPresidentEver;


function bestPresidentEver(a,b){
  //for some reason always returns Trump.
}

 and then call best(a,b) instead of bestPresidentEver(a,b)

I am wondering how to do that opposed to assigning the function to the var upon declaration.

var best = 
function bestPresidentEver(a,b){
  //for some reason always returns Trump.
}

This sounds like an XY problem. What problem are you trying to solve by declaring/referencing a function in this way? — Jordan Running
– Jordan Running, Commented Feb 22, 2017 at 17:16
I am using SignalR, and I need to point it to a function, and I also want to call that function in other areas of the application. — eaglei22
– eaglei22, Commented Feb 22, 2017 at 17:18

beta-developper · Accepted Answer · 2017-02-22 17:39:59Z

1

Declare your variable like this

var bestPresidentEver= function (a,b){
    //for some reason always returns Trump.
    return "Trump"; //:D
}

Then call that function like this

//You have to declare a and b variables
var trumpHere = bestPresidentEver(a,b);

If your function is already declared, just assign it to the variable :

function bestPresidentEver (a,b){
    //for some reason always returns Trump.
    return "Trump"; //:D
}

var trumpHere = bestPresidentEver;

Then call it like this :

var trumpAgain = trumpHere(a, b);

edited Feb 22, 2017 at 17:39

answered Feb 22, 2017 at 17:17

beta-developper

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7 Comments

beta-developper Over a year ago

You have to declare this variable/function before calling it, or you will get an error undefined variable bestPresidentEver

Scott Marcus Over a year ago

It's general convention to only use a $ as the leading character in an identifier when that identifier is a library object, like a JQuery object.

beta-developper Over a year ago

I know :D, but this is Trump we talking about :D

Scott Marcus Over a year ago

You can call a function declaration before the declaration due to hoisting. You can't call a function assigned to a variable until after the function has been declared.

eaglei22 Over a year ago

Perfect, just what I was looking for. Thank you @Ayaou!

|

Nick · Accepted Answer · 2017-02-22 17:45:10Z

1

If the variable exists and it's not a const you can simply reassign it's value to the function itself. Ex

var foo = 'foo';
function bar(a) {
  return 'example ' + a;
}
bar('code'); //=> "example code"

/* Further down, reassign the `foo` variable */
foo = bar;
foo('code, again'); //=> "example code, again"

I am using SignalR, and I need to point it to a function, and I also want to call that function in other areas of the application.

If the library expects a function parameter, you can simply pass that function like so.

function first(next /* expects a function parameter */) {
  return next('hello');
}

function second(prefix) {
  return prefix+ ' world!';
}
first(second); //=> "hello world!"

answered Feb 22, 2017 at 17:45

Nick

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2 Comments

eaglei22 Over a year ago

Thanks Nick, the way SignalR expects the function is like this, $connection.Hub.client.YouPickNameOfFunction = function(a,b){}; I am still learning Javascript and can do a lot of things with it, but I was stuck understanding how to point an already declared function (with parameters) to a variable, as I haven't had to do this before, and I couldn't find a clear answer just searching. I was going to drop the function call in the anonymous functions, but I wanted to do things most efficient.

Nick Over a year ago

All you have to do in this case is what I showed in the first code block. The parameters you'll pass when you call the function (or will be passed by the library when it calls it itself if such is performed). However, if you want to specify values for those parameters prior to the fn being called, you need to use Function.prototype.bind

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